This invention relates to high power lasers and more particularly to a method of reducing arcing in a high power gas transport laser.
The gas transport laser as described in U.S. Pat. No. 3,772,610, assigned to the assignee of this invention, is capable of generating output powers in the order of 1 KW or greater by means of a continuous electrical discharge across the flowing gas in the laser cavity. This discharge energizes the molecules of the CO.sub.2 mixture which ultimately causes the gas to lase and produces the coherent laser output beam. The gas mixture is recirculated, cooled and returned to the active lasing region in a closed circuit fluid path. The gas mixture typically comprises 78% (by volume) helium, 18% nitrogen, 4% carbon dioxide. The cathode is a straight smooth preferably copper tube extending transversely of the direction of the gas flow and the anode comprises a plurality of conductive pads coextensive with the cathode and connected to the electrical circuits through ballast resistors which control the uniformity of current over the area of the electrodes.
While this laser has performed successfully in the field in producing continuous wave output beams at high powers, a problem has been experienced in that after approximately twenty hours of continuous operation a cupric oxide coating or layer forms on the cathode surface and causes arcing between the electrodes. In addition, a cuprous oxide film forms around the edges of the active area of the cathode but does not seem to be detrimental to performance of this electrode. The cupric oxide is detrimental, however, due to its low thermal conductivity and thick build-up. This produces hot spots on the cathode which promote arcing. Such cupric oxide build-up has necessitated shut down of the laser, removal of the cathode from the laser, sanding of the oxide layer from the cathode surface, repolishing the cathode surface and replacing the cleaned cathode in a laser. This is time consuming and costly and adversely affects the use of this laser in production operations requiring long intervals of uninterrupted laser service.